摘要： Metal-halide perovskites as absorber materials for solar cells have captured the attention of an increasing number of scientists over the last years. As is common for most photovoltaic technologies, early stages of solar cell development were dedicated to understanding and tuning the properties of materials and interfaces in the perovskite-based solar cells to ensure efficient charge separation and suppress unwanted recombination channels. However, when photovoltaic technologies become more mature, the design of optical properties of materials, interfaces, and complete device stacks becomes increasingly important in order to come even closer to the efficiency limits dictated by thermodynamics. This Viewpoint is dedicated to briefly discuss how photons can be absorbed more efficiently, be reused, be distributed between different cells in tandem devices, and finally be used as a means to characterize the electronic properties of materials and interfaces. More detailed discussions of these topics can then be found in a series of Perspective articles on topics related to the optical properties and the optical design of perovskite-based solar cells that are introduced in this Viewpoint.